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Boran et al. (2016). “Cellulose HDPE composites,” BioResources 11(4), 8178-8199. 8178
Characterization of Ultrafine Cellulose-filled High-Density Polyethylene Composites Prepared using Different Compounding Methods
Sevda Boran,a,*Alper Kiziltas,b,c Esra Erbas Kiziltas,b,d and Douglas J. Gardner b
An extensional flow mixture (EFM) system was studied, with the goal of achieving better distributive and dispersive mixing. The effects of different mixing strategies (masterbatch method (MB), polyethylene-grafted maleic anhydride (PE-g-MA) as a compatibilizer, and compounding devices, such as a single screw extruder (SSE), a twin screw extruder (TSE), and an extensional flow mixer (EFM)) on the mechanical, thermal, rheological, and morphological properties of ultrafine cellulose (UFC)-filled high-density polyethylene (HDPE) composites were investigated. Maximum tensile strength (17.7 MPa), tensile modulus (0.88 GPa), flexural strength (18.8 MPa), and flexural modulus (0.63 GPa) were obtained from the MB compounding method. The maximum stress-strain (13.8%) was obtained with EFM compounding. Polymer composites from SSE and SSE/EFM compounding methods with PE-g-MA exhibited slightly higher crystallinity compared with other compounding methods. The storage modulus of the samples prepared with the MB method was higher than those prepared with the SSE compounding method. The UFC-filled HDPE composites from the EFM compounding process exhibited lower melt viscosities than the other composites at high shear rates. Scanning electron microscopy (SEM) images showed the cellulose to be distributed and dispersed reasonably well in the HDPE matrix when using a coupling agent in combination with the MB and EFM compounding methods.
Keywords: Composites; Cellulose; Mechanical properties; Rheology; Extrusion
Contact information: a: Department of Woodworking Industry Engineering, Faculty of Technology,
Karadeniz Technical University, 61830 Trabzon, Turkey; b: Advanced Structures and Composites Center,
University of Maine, 04469Orono, ME; c: Department of Forest Industry Engineering, Faculty of Forestry,
University of Bartın, 74100Bartın, Turkey; d: The Scientific and Technological Research Council of Turkey
(Tubitak), Tunus Cad, Kavaklıdere, 06100 Ankara, Turkey;
* Corresponding author: [email protected]
INTRODUCTION
In recent years, the use of renewable cellulose for polymer composites has attracted
much attention as an environmentally friendly natural material. Cellulose-based micro- and
nanomaterials are considered alternatives to inorganic filler-reinforced thermoplastic
polymer composites for construction, automotive, and packaging applications (Yang and
Gardner 2011; Endo et al. 2013; Abdul Khalil et al. 2014). These new materials can provide
strong reinforcement in polymer composites (Henriksson et al. 2007; Ramires and
Dufresne 2011). Micro- and nanocellulose has favorable features, such as renewability,
biodegradability, high surface area, high modulus, high strength, and low density, in
comparison to commercial fillers (e.g., talc and glass fibers). Micro- and nanocellulose
have been used in many applications, including reinforcement of transparent polymers, thin
films of polymer electrolytes for lithium battery applications, and optoelectronic devices
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Boran et al. (2016). “Cellulose HDPE composites,” BioResources 11(4), 8178-8199. 8179
(Hitoshi and Akira 2007; Khalil et al. 2012; Ozen et al. 2013; Pandey et al. 2013). In spite
of some advantages, these renewable materials have undesired properties, such as limited
thermal stability at typical melt processing temperatures of approximately 200°C, limited
compatibility with many thermoplastic matrices attributable to their highly hydrophilic
properties, poor dispersion characteristics in the non-polar thermoplastic melt because of
strong hydrogen bonding forces between the fibers, and high moisture absorption of the
fibers affecting the dimensional stability of the composite materials (Khalil et al. 2012;
Kiziltas et al. 2013; Pandey et al. 2013).
The key challenge to uniform compounding is providing uniformly distributed and
disperse mixing of fillers in polymer matrices (Rauwendaal 1998; Wang and Zloczower
2001). Composites reinforced with micro- and nanocellulose have excellent mechanical
properties compared to other biomaterials, such as wood fiber and agricultural wastes
(Walther et al. 2010; Josefsson et al. 2014). It has been reported that the processing method,
the morphology and dimensions of the cellulose, the microstructure of the matrix, and the
matrix/filler interaction all influence the mechanical properties of cellulose
nanocomposites (Ramires and Dufresne 2011). It is especially important to develop
methods and procedures for the uniform dispersion of micro- and nanocellulose in non-
polar polymer matrices, such as polyethylene (PE), polypropylene (PP), and polylactic acid
(PLA) (Balatinecz et al. 1999; Caulfield et al. 2001; Kiziltas et al. 2016a,b). Recently, PE-
based micro- and nanocomposites have received considerable interest in electrical
insulation, biomedicine, packaging, construction, furniture, aerospace, and automotive
applications (Panaitescu et al. 2007a; Pöllänen et al. 2013). Previously, cellulose-based
micro- and nanomaterials have been used as fillers in PE matrices (Bataille et al. 1990;
Herrera-Franco and Aguilar-Vega 1997; Panaitescu et al. 2007b; Tajeddin et al. 2009;
Shumigin et al. 2011; Sdrobiş et al. 2012; Pöllänen et al. 2013; Kiziltas et al. 2016a). The
cellulose-filled PE composites are melt-mixed using a Brabender mixer, a conical twin-
screw microcompounder, and a twin-screw extruder (TSE) (Shumigin et al. 2011; Sdrobiş
et al. 2012; Kiziltas et al. 2016a). The chemical compatibility of hydrophilic cellulose and
hydrophobic PE, in addition to the cellulose dispersion in PE matrices, have been improved
with the addition of a coupling agent, chemical treatment of the cellulose surface, and a
carrier system for cellulose-filled PE micro- and nanocomposites (Sdrobiş et al. 2012;
Pöllänen et al. 2013; Kiziltas et al. 2016a).
Single-screw extruders (SSE), twin-screw extruders (TSE), and extensional flow
mixers (EFM) are used to compound micro- and nanocomposite materials and enhance
dispersion of micro- and nanoscale fillers in different polymer matrices (Li et al. 2007;
Utracki 2007; Boran et al. 2016). The formulations are exposed to strong extensional flow
fields in EFM. The elongational stress in EFM is generated in the gap space between the
convergent-divergent (C-D) plates controlled by the geometry of the mixing cavity. These
C-D plates have an adjustable gap, a hyperbolic convergence to direct the compound
aggregates in the flow direction, and a divergent part to randomize the flow. The geometry
of the C-D plates in EFM provides the balance of the extensional to shear stress from within
the C-D plates (Li et al. 2007). The EFM method has the following advantages: the mixture
of the two fluids is exposed to strong extensional flow fields; a series of holes are replaced
by slits to decrease the pressure drop; the flow fields are occurring through a series of
divergences and convergences of increasing intensity; the slit gaps are adjustable (Utracki
et al. 2003) so that the flow can be controlled by the geometry of the mixing cavity (Nguyen
and Utracki 1995; Luciani and Utracki 1996; Bourry et al. 1999). Currently, the most
homogenous dispersion of nanofiller within the polymer matrix is usually achieved by MB
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Boran et al. (2016). “Cellulose HDPE composites,” BioResources 11(4), 8178-8199. 8180
compounding, combined with SSE and EFM. Nevertheless, this approach has not been
investigated for nanocellulose-reinforced thermoplastic composites.
As previously mentioned, the primary problem associated with micro- and nano-
composites is their ability to obtain a homogeneous dispersion of fillers within the polymer
matrix (Prashantha et al. 2009). The homogenous dispersion of micro- and nanoparticles
is difficult within a polymer blend. The MB compounding method is a concentrated
mixture of fillers encapsulated during melt compounding into a carrier resin and one of the
simplest and is one of the most economical methods in processing of micro- and
nanoparticles in composites. This method has been applied to overcome the shortcomings
of filler homogeneity and to improve processing characteristics, physical, and mechanical
properties of composites (Lee et al. 2008; Joo et al. 2011). Importantly, the dispersion of
micro- and nanocellulose in MBs should be investigated and the dilution process should be
carried out under appropriate processing conditions to obtain a well-dispersed micro- and
nanocellulose PE matrix, as seen in multi-wall carbon nanotube nanocomposites
(Prashantha et al. 2009). It is also necessary to understand the effects of cellulose and
compatibilizers on the mechanical, thermal, and rheological properties of polymer/
cellulose composites (Lee et al. 2008). To obtain nano/micro cellulose-based thermoplastic
composites with acceptable mechanical properties, the filler dispersion within the matrix
is a key criterion in non-polar polymer matrices, such as PE and PP. For example, cellulose-
filled PE composites are typically melt-mixed in a Brabender mixer, conical twin-screw
extruder, or SSE. Another way to enhance the dispersion of nano- and micro-fillers within
the matrix is the use of SSE, TSE, and EFM, which is rather rare. Chemical compatibility
between hydrophilic cellulose filler/reinforcement and hydrophobic polymer matrix, such
as PE, has been improved with coupling agents or chemical treatment of the filler’s surface.
Improved compatibility between the matrix and the filler typically leads to better filler
dispersion within the polymer matrix. Furthermore, the role of the coupling agent to
improve the dispersion of cellulose in PE and its adhesion towards the polymer matrix, as
well as the EFM compounding method, has yet to be thoroughly examined.
In this study, the HDPE/ultrafine cellulose (UFC) composites were produced by
different compounding methods, including single-pass extrusion and MB compounding
methods with or without EFM. The composites were characterized to determine their
mechanical, thermal, and rheological properties.
EXPERIMENTAL Materials
The HDPE powder was supplied in the form of polymer pellets by Equistar
(Houston, Texas, USA), and PE-g-MA, the compatibilizer, was obtained from the
Polybond Co. (Greensboro, North Carolina, USA). The ultrafine cellulose powder (UFC),
with an average particle size of 8 µm, was supplied by J. Rettenmaier & Sohne (Rosenberg,
Germany). The materials’ properties are listed in Table 1. The extensional flow mixer
(EFM) was attached to SSE in an attempt to obtain the best polymer mixing and dispersing.
The EFM was adjusted with a gap between the C-D plates and set as h=20 µm after
pretesting.
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Table 1. Material Properties
*PE-g-MA: Polyethylene-grafted maleic anhydride
Methods Masterbatch(MB)method
The HDPE and UFC had an initial moisture content (MC) of approximately 6%.
The HDPE and UFC were dried for a minimum of 16 h until they reached below 1% MC
in an oven at 80 °C. All moisture measurements were performed according to the ASTM
D 5229 M14 (2014) testing standard. First, the HDPE powder was mixed with the UFC by
thermal compounding using a C.W. Brabender Prep-mixer® (South Hackensack, NJ,
USA) with a bowl mixer to obtain a MB containing 10% UFC. The mixer temperature was
set at 160 to170 °C, with a melting temperature of 170 to 180 °C, and a rotor speed of 60
rpm. The procedure for the MB compounding method was as follows: the reaction chamber
was heated to 180 °C and the mixer was set at 60 rpm; then, the HDPE powder was fed
into the chamber; the HDPE powder was completely melted after 5 min; the UFC was
slowly added to the HDPE melt; the system was kept closed for 5 min; after the thermal
mixer was stopped, the blending material obtained was removed from the mixing system.
In the second step, the MB was diluted to 4 wt.% UFC. The dilution was performed
using a SSE (Davis-Standard, Pawcatuck, North America, USA) or a SSE/EFM. Based on
our preliminary results, the EFM was adjusted with the gap between the C-D plates at h=20
µm. The PE-g-MA was premixed with other materials before the extrusion process. The
extrudate was solidified directly in an air-cooling system after the SSE or SSE/EFM
process while being pulled with a 2201 Series End Drive Conveyor from Dorner MFG
Corp. (Hartland, WI, USA). The solidified extrudate was pelletized using a pelletizer for
the laboratory extrusion runs from C.W. Brabender Instruments, Inc. (South Hackensack,
New Jersey, USA). The processing parameters for the MB compounding method are shown
in Table 2.
Single pass method
The UFC and PE-g-MA were dried in an oven at 80°C overnight before melt
compounding. The HDPE powder, PE-g-MA, and UFC were premixed concurrently,
placed in the extruder feed hopper, and then into a speed mixer. The sample was extruded
at 60 rpm using a C.W. Brabender 20 mm clamshell segmented twin screw extruder,
attached to the Intelli-Torque Plastic-Corder drive system (C. W. Brabender Instruments,
(South Hackensack, New Jersey, USA)) for TSE and the screw configuration of the system
was the stand-alone TSE20/40D version. The same pelletizer and cooling systems were
used. The processing parameters are shown in Table 2.
Material /Trade name Diameter
(µm)
Melt Flow Index(MFI) (g/10 min)
Density (g/cm3)
Melting Point (MP)
(°C) Supplier
UFC/ Arbocel® UFC 100
8 - 1.56 - JRS
High Density Polyethylene (HDPE) /MicrotheneMP655962
300-500 5 0.95 128 Equistar
PE-g-MA/ Polybond® 3029
- 4 0.96 130 Polybond
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Table 2. (a) Temperature (°C) Profile for the SSE, TSE, and EFM; (b) Processing Conditions used in Injection Molding, SSE, and TSE Compounding
a) Single-screw extruder(SSE)
Zones Z-1 Z-2 Z-3 Z-4 Clamp Die
Temp. (°C) 145 145 150 150 160 170
a) Twin-screw extruder(TSE)
Zones Z-1 Z-2 Z-3 Z-4 Z-5 Die
Temp. (°C) 145 145 150 150 160 170
a)Extensional flow mixer(EFM)
Zones Z-1 Z-2 Z-3
Temp. (°C) 190 200 200
b) Process parameters
Twin screw speed (rpm) 60
Single screw speed (rpm) 50
Injection pressure (MPa) 17
Holding time (s) 10
Cooling time (s) 10
Injection mold temperature (°C) 180
Injection barrel temperature (°C) 180
Table 3 shows the composition and designation of UFC-filled HDPE polymer
composites. The SSE, SSE/EFM, and TSE samples are also symbolized as S, E, and T,
respectively (Table 3). The weight ratio of UFC to PE-g-MA was held constant at 1:2
throughout this study, based on the preliminary findings. For mechanical testing, the
pelletized samples were dried at 80 °C overnight before being injection molded All samples
were injection molded using a barrel temperature of 180 °C, mold temperature of 180 °C,
and injection pressure of 17 MPa.
Table 3. Composition and Designation of UFC-filled PE Polymer Composites
Sample Designation
High Density Polyethylene
(HDPE)
Polyethylene graft maleic anhydride (PE-g-MA)
(wt.%)
Ultrafine cellulose
(UFC) (wt.%)
Processing method
S 100 - - SSE
S/E 100 - - SSE/EFM
C/S 96 4 - SSE
UFC/S 96 - 4 SSE
UFC/T 96 - 4 TSE
UFC/S/E 96 - 4 SSE/EFM
UFC/S/MB 96 - 4 SSE/MB
UFC/S/E/MB 96 - 4 SSE/EFM/MB
UFC/C/S 88 8 4 SSE
UFC/C/S/E 88 8 4 SSE/EFM
UFC/C/S/MB 88 8 4 SS/MB
UFC/C/S/MB/E 88 8 4 SSE/MB/EFM
SSE: Single-screw extruder; TSE: Twin-screw extruder; EFM; Extensional flow mixer; UFC: Ultrafine cellulose; MB: Masterbatch; C: Coupling agent
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Mechanical Tests All the mechanical tests were carried out in an environmentally controlled room at
23 ± 2 °C and 50±5% relative humidity.
Tension testing
The tensile tests were performed using an Instron 5966 (Norwood, MA, USA) with
a 10-kN load cell at a crosshead speed of 5 mm/min, according to ASTM D638-10 (2010).
The dimensions of specimens were selected as 5x13x165 mm. The elongation of the tested
specimen was determined with an extensometer. The modulus was determined according
to the slope. The tensile strength was determined as the maximum load divided by the
initial cross-sectional area. A minimum of six samples were tested for each composition,
coupled with the relevant processing method, and the samples were pooled.
Flexural testing
Flexural tests of the samples were performed according to ASTM D790-10 (2010).
The flexural tests were conducted using an Instron8872 (Norwood, MA, USA) with a 1-
kN load cell. The size of samples was 5 mm x13 mm x120 mm. The support span was 50
mm. The sample was placed on two supporting pins and set a specified distance apart. The
test was stopped when the specimen broke before 5%. All of the samples were tested at a
loading rate of 1.25 mm/min. At least six specimens were tested for each composition. The
flexure test results are depicted as the mean of all tested samples.
Izod impact test
The notched Izod impact tests according to ASTM D256 (2010) were carried out
using a Resil 50 B impact testing machine (Ceast®, Akron, Ohio, USA). The specimens
were prepared at 5 mm x 13 mm x 65 mm. These specimens were clamped to the bottom
of the test fixture. The hammer of this test machine was 2.75 J, and this hammer was
released from a specified height. The depth under the sample width and the notch were
entered before the machine recorded the energy required to break the test sample. A
minimum of 10 samples were tested from each composition and the test results were
reported the mean of all of the tested samples.
Differential scanning calorimetry (DSC)
Differential scanning calorimetry was performed on a TA Q2000 (TA Instruments,
New Castle, USA) analyzer, and a sample weight of 8 to10 mg was used to measure the
thermal transitions of composites, including the crystallization temperature (Tc), melting
temperatures (Tm), and enthalpy of transitions(ΔH). The samples were equilibrated at 25
°C for 5 min, and then heated at a rate of 20 °C/min to 200 °C. Then, the samples were
held for 5 min to erase thermal history, and cooled at a rate of 10 °C/min to 0 °C. Next, the
samples were held for 5 min and heated at a rate of 10 °C/min to 200 °C. All of these
procedures were performed under a nitrogen atmosphere. The melting temperatures (Tm)
were determined from a second scan, and Tm was recorded as the peak temperature of the
melting endotherm.
The ‘all samples’ crystallinity (Xc) index, which is an indication of the amount of
crystalline region in the polymer with respect to amorphous content, was calculated as
follows (Kiziltas et al. 2013),
𝑋𝑐 =∆𝐻𝑓 × 100
∆𝐻°𝑓 × 𝜔
(1)
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Boran et al. (2016). “Cellulose HDPE composites,” BioResources 11(4), 8178-8199. 8184
where ΔHf is the heat of fusion of the neat HDPE and composites, ΔH°f is the heat of
fusion for 100% crystalline HDPE (ΔH100=287.3 J/g), and ω is the mass fraction for
HDPE in the composites (Mirabella and Bafna 2002). The results were calculated as the
mean of three samples.
Rheology
Rheological properties of the composites were measured by a stress-controlled
Bohlin Gemini rheometer (Aimil Ltd., New Delhi, USA) with a parallel plate fixture (25
mm diameter) at a temperature of 180 °C. The gap between the two parallel plates was
maintained at 2 mm to calculate the storage moduli (G′). All of the samples were set
between the parallel plates after loading. The rheological measurements were used to
determine the dynamic complex viscosity (|η|*), the storage and loss moduli (G′ and G′′),
and the loss factor (tan δ) to evaluate of the rheology properties of the samples. A strain of
1% was used to ensure all measurements were tested within the linear viscoelastic range
for each sample (Kiziltas et al. 2013).
Scanning electron microscopy (SEM)
Scanning electron micrographs were used to assess the degree of cellulose
dispersion within the PE matrix. Test specimens were immersed in liquid nitrogen and
fractured. The fractured surfaces were gold sputtered and inspected on a ZEISS EVO LS
10 (North Chesterfield, VA, USA) scanning electron microscope. The SEM images were
recorded at 10 kV using 2000X magnification.
Statistical analysis
Differences among treatment groups were analyzed using one-way analysis of
variance (ANOVA) and the means were separated using the Tukey-Kramer (HSD) method
of pair wise comparison if the overall ANOVA model was significant (P<0.05) (JMP
Statistical Discovery Software Version 8).
RESULTS AND DISCUSSION
Mechanical Properties Table 4 indicates the mechanical properties of the neat HDPE- and UFC-filled
HDPE composites. UFC/C/S/MB method resulted in a maximum tensile strength of 17.7
MPa. The tensile strength of the samples ranged from 15.3 MPa to 17.7 MPa. When the
coupling agent was introduced, the tensile strength for all of the compounding methods
improved considerably. It is known that coupling agent strengthens cellulose-based
polymer composites and decreases the moisture absorption of cellulose fibers (Botros
2003). The effect of PE-g-MA on the mechanical properties of microcrystalline cellulose
and viscose fibers was also studied by Pöllänen et al. (2013). They found that PE-g-MA
increased the tensile strength by increasing the adhesion between the filler and the HDPE
matrix, based on SEM results (Pöllänen et al. 2013). Tokihisa et al. (2006) declared that it
was unclear why the SSE/EFM compounding method increased performance because of
better dispersion compared with the TSE/EFM compounding method. It is known that
better dispersion was obtained under mild compounding conditions (Dennis et al. 2001;
Tokihisa et al. 2006).
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Table 4. Mechanical Properties of the Neat HDPE- and UFC-filled HDPE Composites
Samples Tensile properties Flexural properties
I.S. (J/m)
ε (%)
σt
(MPa) Et
(GPa) Ef
(GPa) σf
(MPa)
S 13.4 (bc) (0.5)
16.3 (d) (0.5)
0.78(abcd) (0.07)
0.51 (de) (0.02)
15.7 (f) (0.4)
127.4 (b) (11.1)
S/E 15.3 (a)
(0.5) 15.7 (e)
(0.3) 0.72 (cd)
(0.05) 0.53 (d) (0.02)
16.0 (ef) (0.2)
155.5 (a) (15.2)
C/S 12.0 (ef)
(0.4) 17.1 (bc)
(0.2) 0.84 (ab)
(0.09) 0.53 (d) (0.01)
16.1 (ef) (0.3)
140.2 (b) (12.7)
UFC/S 13.3 (bcd) (0.3)
15.5 (e) (0.1)
0.75 (bcd) (0.03)
0.50 (e) (0.01)
15.5 (f) (0.3)
68.7 (c) (5.7)
UFC/T 13.7 (b)
(0.2) 15.8 (de)
(0.3)
0.78 (abcd) (0.04)
0.57 (c) (0.01)
17.2 (cd) (0.1)
70.5 (c) (2.8)
UFC/S/E 13.8 (b)
(0.3) 15.9 (de)
(0.3) 0.83 (ab)
(0.04) 0.61 (ab)
(0.01)
17.8 (abcd) (0.2)
59.8 (cd) (2.9)
UFC/S/MB 13.2 (bcd) (0.5)
15.5 (e) (0.1)
0.82 (abc) (0.05)
0.53 (d) (0.02)
16.7 (de) (0.2)
62.9 (c) (6.3)
UFC/S/MB/E 13.3 (bcd) (0.7)
15.6 (e) (0.2)
0.81(abc) (0.05)
0.59 (bc) (0.01)
17.8 (abc) (0.1)
60.6 (cd) (3.1)
UFC/C/S 12.7 (cde) (0.4)
17.3 (ab) (0.2)
0.69 (d) (0.02)
0.58 (bc) (0.01)
17.8 (bc) (0.2)
63.4 (c) (5.7)
UFC/C/S/E 11.9 (ef)
(0.2) 17.2 (bc)
(0.1) 0.87 (a) (0.02)
0.59 (bc) (0.01)
17.3 (cd) (0.3)
71.4 (c) (4.6)
UFC/C/S/MB 11.5 (f)
(0.5) 17.7 (a)
(0.3) 0.75 (bcd)
(0.05) 0.63 (a) (0.01)
18.8 (a) (0.2)
49.8 (d) (4.6)
UFC/C/S/MB/E 12.6 (de) (0.4)
16.8 (c) (0.2)
0.88 (a) (0.04)
0.61(ab) (0.02)
18.4 (ab) (0.1)
50.1 (d) (4.8)
*The values in the parentheses are standard deviations **Means with the same letter for each property were not significantly different at the 5% significance level ε: Strain at the maximum stress
The addition of the coupling agent to the EFM compounding method resulted in a
better tensile modulus than the UFC/C/S and UFC/C/S/MB compounding methods. The
EFM attachment to the SSE provided a better tensile modulus than the UFC/S
compounding method. Combining SSE and MB demonstrated a minor improvement in the
tensile modulus over the MB only method. It has been reported that clay-containing
polymeric nanocomposites using SSE/EFM compounding resulted in better dispersion and
mechanical performance compared with TSE (Utracki 2007). Some researchers have
reported that using a MB compounding method results in better material property through
precise control of filler concentration in terms of mechanical properties. The MB
compounding method ensures better dispersive mixing, more uniform exfoliated structure,
and less reduction of the deformation properties compared with direct compounding
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(Lopez-Quintanilla et al. 2005; Li et al. 2007; Treece et al. 2007; Etelaaho et al. 2009).
Masterbatch compounding with cellulose nanocrystal (CNC)/polycarbonate (PC),
CNC/acrylonitrile-butadiene-styrene (ABS), and microcrystalline cellulose (MCC)/PP
have been prepared in previous studies (Spoljaric et al. 2009; Ma et al. 2015; Mariano et
al. 2015). Nevertheless, the UFC/S/MB/E compounding method produced a lower tensile
modulus than the UFC/S/E compounding method. There is limited information regarding
MB dilution on the mechanical properties of polymer composites using ultrafine cellulose.
However, it is known that cellulose acts as a mechanical reinforcement of the polymer.
When a composite is filled with cellulose, the tensile modulus of the polymer composite
improves considerably (Mathew et al. 2005; Petersson and Oksman 2006; Kiziltas et al.
2010). Polymer composites can be affected by filler dispersion and size of the cellulose
fiber particles in the polymer matrix. It is known that the reinforcing ability of cellulose
micro- and nanoparticles results from their high surface area and good mechanical
properties; however, cellulose micro- and nanoparticles should be well-dispersed in the
polymer matrix to achieve notable increases in mechanical properties. Their small size does
not generate large stress concentrations in the polymer matrix, so well-dispersed cellulose
particles can improve tensile properties (Kvien et al. 2005; Kvien and Oksman 2007; Yang
et al. 2011). Further evidence on the agglomeration and dispersion of UFC samples with
MB and EFM compounding into the polymer matrix will also be discussed in the next SEM
analysis section. Microscopic observation also showed that the cellulose was well
distributed and dispersed in the HDPE matrix when using a coupling agent and the MB or
EFM compounding methods. Therefore, the addition of MB or EFM to the compounding
method can be advised.
Table 4 illustrates the strain at the maximum stress change in UFC-filled HDPE
composites using SSE, TSE, SSE/EFM, SSE/MB, SSE/MB/EFM, and each of these
compounding methods included the addition of a coupling agent, excluding TSE. The
maximum value for strain at the maximum stress was achieved from the S/E compounding
method, while the minimum value was observed from the UFC/C/S/MB with the coupling
agent. The highest value for strain at the maximum stress was 13.8%. When compared to
the MB compounding method, the UFC/S/MB/EFM without the coupling agent produced
the maximum strain value. All samples produced with the coupling agent exhibited lower
strain at the maximum stress than the compounding methods without the coupling agent
because of the enhanced adhesion between the UFC and the HDPE matrix. Similar results
were reported by Shao et al. (2015) and Ismail et al. (2001) for triethoxysilane (AS),
methacriloxy propyl trimethoxy silane (MS), and maleic anhydride-grafted polypropylene
(MAPP)-treated natural fiber (cellulose, sawdust, and wheat straw), and reinforced PP and
silane-treated white rice husk ash-filled PP/natural rubber composites, respectively (Ismail
et al. 2001; Shao et al. 2015). Shao et al. (2015) explained that better adhesion yields more
restriction of deformation capacity of composites; therefore, catastrophic failure occurs
after small strain deformations. The highest values of strain at the maximum stress for all
combinations of EFM compounding were obtained from the UFC/S/E compounding
method without the coupling agent. The elongational flow in EFM provides excellent
mixing, decreased viscous dissipation and lower melt temperatures, dispersed at large
viscosity ratios, and enhanced distributive mixing. The SSE exhibited poor dispersive
mixing capability compared with TSE.
There are two important differences between TSE and SSE in terms of the mixing
mechanism. The flow in high-stress regions (HSR) of most mixers is predominantly shear
flow and the fluid elements pass through the HSR only once in SSE compounding. In TSE
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compounding, the flow in the kneading disks has a strong elongational flow and the fluid
elements passes through the HSR several times (Rauwendaal et al. 1999). However, the
use of EFM shows that the mixture of two compounds is exposed to strong extensional
flow fields because the flow fields are generated by a series of convergences and
divergences (Nguyen and Utracki 1995; Utracki 2003). The EFM compounding method
has some advantageous for distributive and dispersive mixing. Distributive mixing in EFM
compounding is more efficient because the interfacial area is much higher than in the shear
flow. Consequently, dispersive mixing is also much higher than that of shear because the
drop deformability in elongation is several times higher than in shear (Tokihisa et al. 2006).
Some researchers also reported favorable mechanical properties in a well-dispersed
nanocomposite with cellulose nanofibrils (Walther et al. 2010; Josefsson et al. 2014).
The best flexural strength and flexural modulus values were obtained from the
UFC/C/S/MB compounding method. Flexural strength values ranged from 15.5 to 18.8
MPa, while the flexural modulus ranged from 0.50 to 0.63 GPa. It was obvious that the
EFM compounding method improved the flexural properties of the ultrafine cellulose-
filled composites compared to UFC/T, UFC/S, and UFC/S/MB compounding methods.
Using the MB compounding method had a beneficial role in improving the flexural
strength. The addition of the coupling agent to UFC/S and UFC/S/MB compounding
methods resulted in better flexural properties. Li et al. (2007) studied the effects of mixing
strategies (with or without MB compounding method), and processing devices (TSE, SSE,
and SSE/EFM) for PP-based clay nanocomposites. As a result, the flexural properties of
the samples prepared from MB compounding were better than those from the single-pass
method (Li et al. 2007).
As shown in Table 4, the maximum value for the impact strength was obtained from
the UFC/C/S/E compounding method. When using EFM compounding without the
coupling agent, the impact strength decreased slightly. However, it is noteworthy to
mention that using the coupling agent had less of an impact on the strength value in
comparison with UFC/S, UFC/S/MB, UFC/S/MB/E compounding methods. The results
also indicated that using the MB compounding method produced lower impact strength
values than the UFC-filled HDPE composites prepared from different compounding
methods, excluding the UFC/S/MB/E method. Similar results were also reported by Li and
Chen (2007) for HDPE/expanded graphite nanocomposites prepared via MB
compounding. The lower impact strength can be explained by the lower interaction made
by MB than the other UFC-filled HDPE composites prepared by different compounding
methods (Li and Chen 2007).
Differential Scanning Calorimetry Analysis Differential scanning calorimetry measurements were used to characterize the
thermal properties of UFC-filled HDPE composites prepared by various compounding
methods. Melting and crystallization temperatures of the specimens did not notably affect
the outcomes. Šumigin et al. (2012) declared that crystallization and melting temperatures
of the low density polyethylene (LDPE) and LDPE with cellulose do not change with
cellulose content. Table 5 shows that the crystallization temperatures were between 116
and 118 °C, while the melting temperatures were approximately 129 °C. Using of the MB
compounding method resulted in a small decrease in the melting and crystallization
enthalpy for all of the polymer composites. The DSC results showed that the addition of
the coupling agent influenced the HDPE melting and crystallization enthalpies for UFC/S
and UFC/S/E compounding methods. Araujo et al. (2008) also found that the coupling
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agent affected the melting and crystallization behavior of natural fiber-reinforced PE
composites. The degree of crystallinity of all composites was also calculated in Table 5.
There was a minor reduction in the degree of crystallinity for the MB compounding
methods. The UFC/S and UFC/C/S/E methods exhibited a slightly higher degree of
crystallinity compared to the other compounding methods.
Table 5. Melting and Crystallization Parameters of the Neat HDPE and UFC-Filled Composites
Samples Melting temperature
(Tm) (°C)
Crystallization temperature(Tc)
(°C)
Enthalpy of melting
(ΔHm)
(J/g)
Enthalpy of crystallization
(ΔHc)
(J/g)
Crystallinity (Xc) (%)
S 130.1 (0.3) 116.4 (0.4) 181.4
(1.9) 182.5 (2.4) 65.5 (1.7)
S/E 129.7 (0.1)
116.1 (0.1) 180.6 (2.2)
180.7 (1.6) 65.2 (2.2)
C/S 129.9 (0.1)
116.8 (0.3) 182.8 (3.2)
181.6 (3.1) 66.0 (4.2)
UFC/S 129.2 (0.2) 117.0 (0.2)
178.8 (1.4) 178.8 (1.1) 67.2 (1.4)
UFC/T 129.6 (0.0) 115.8 (0.2)
176.0 (3.5) 175.2 (3.4) 66.2 (3.5)
UFC/S/E 129.8 (0.0) 116.6 (0.4)
173.5 (0.0) 175.6 (0.0) 65.2 (3.5)
UFC/S/MB 129.5 (0.1) 116.7 (0.2)
172.6 (3.2) 171.9 (3.0) 64.9 (3.3)
UFC/S/MB/E 129.6 (0.2) 118.6 (1.5)
169.8 (0.6) 170.7 (2.0) 63.8 (4.9)
UFC/C/S 129.5 (0.2) 117.6 (0.4)
180.3 (4.9) 183.5 (1.9) 67.8 (3.5)
UFC/C/S/E 129.9 (0.2) 117.4 (0.5)
179.0 (3.5) 181.4 (1.8) 67.3 (3.5)
UFC/C/S/MB 129.7 (0.4) 116.8 (0.4)
168.3 (2.8) 168.7 (2.3) 63.3 (2.8)
UFC/C/S/MB/E 129.3 (0.1) 118.1 (0.1)
169.8 (1.1) 171.6 (1.3) 63.9 (1.1)
*Parentheses indicate standard deviation.
Rheological Properties The storage moduli (G' at 170°C as a function of frequency (ω)) of composites
prepared by single-pass (SP) extrusion (a), compatibilized (b), and MB compounding (c)
methods are shown in Fig.1. The S and S/E exhibited typical melt behavior in the thermal
region; the storage modulus (G') increased with the shear frequency in Fig.1a. The addition
of UFC increased the G' of the composites, especially in the thermal region for UFC/S,
UFC/T and UFC/S/E, which was attributed to the strong cellulose-cellulose particle
interaction. The difference in the storage modulus between composites and neat polymers
(S and S/E) was less distinguishable with increasing frequency because the cellulose
particles were disconnected and the cellulose-cellulose interactions were weaker (Volk et
al. 2015). The samples prepared using the SP method (Fig. 1a) in UFC/S/E composites
exhibited a larger G', while those from TSE and SSE were smaller. The relative magnitude
changes of G' for the UFC/S/E compounding method indicated that the composite was
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dominantly more elastic when the UFC was processed with EFM. Figure 1b shows that all
of the filled systems, with or without the coupling agent, had a higher G' than the neat
HDPE. It was also observed that the coupling agent did not improve the G' of the
composites as compared to the composites from SSE (UFC/S) without the coupling agent.
Furthermore, the G' values of samples prepared by the MB compounding method (Fig.1c)
were higher to those prepared by the SP compounding method. These results indicated that
preparation of cellulose composites from MB obtained a well-dispersed cellulose and
increase melt elasticity (Prashantha et al. 2009).
Frequency (1/s)
0.01 0.1 1 10 100
Sto
rag
e M
od
ulu
s (
Pa
)
1e+1
1e+2
1e+3
1e+4
1e+5
S
S+E
UFC+S
UFC+T
UFC+S+E
Frequency (1/s)
0.01 0.1 1 10 100
Sto
rag
e M
od
ulu
s (
Pa
)1e+1
1e+2
1e+3
1e+4
1e+5
S
C+S
UFC+S
UFC+C+S
UFC+C+S+E
UFC+C+S+MB
UFC+C+S+MB+E
Frequency (1/s)
0.01 0.1 1 10 100
Sto
rag
e M
od
ulu
s (
Pa
)
1e+1
1e+2
1e+3
1e+4
1e+5
S
C+S
UFC+S
UFC+S+MB
UFC+S+E+MB
UFC+C+S+MB
UFC+C+S+MB+E
Fig. 1. Storage modulus G’ at 170 °C for as a function of frequency for a) single pass compounding, b) compatibilized systems, and c) MB compounding
The complex viscosity (η*) of the neat HDPE and the UFC-filled HDPE composites
measured at 170 °C as a function of frequency (ω) is shown in Fig. 2. The complex
viscosities decreased with an increase in ω, indicating shear thinning behavior and
pseudoplastic characteristics of HDPE and the UFC-filled HDPE composites. It was
observed from Fig. 2a that the composites from the SSE (UFC/S) and TSE (UFC/T)
extruders, without the coupling agent, exhibited a reduced shear thinning behavior
compared to the neat HDPE. This reduction in complex viscosity for UFC/S and UFC/T
could have been a result of decreased polymer molecular entanglement density, causing a
small disruption in the polymer chain entanglement network (Hatzikiriakos et al. 2005).
This observation was in agreement with Mukherjee et al. (2013) for microcrystalline-filled
PLA composites. It was also observed that η* was neither similar nor lower than the neat
HDPE for composites, including those with the coupling agent (Fig.2b) and processed with
MB methods (Fig. 2c).
a) b)
c)
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Frequency (1/s)
0.01 0.1 1 10 100
Co
mp
lex
Vis
co
sit
y (
Pa
.s)
1000
S
S+E
UFC+S
UFC+T
UFC+S+E
Frequency (1/s)
0.01 0.1 1 10 100
Co
mp
lex
Vis
co
sit
y (
Pa
.s)
1000
S
C+S
UFC+S
UFC+C+S
UFC+C+S+E
UFC+C+S+MB
UFC+C+S+MB+E
Frequency (1/s)
0.01 0.1 1 10 100
Co
mp
lex
Vis
co
sit
y (
Pa
.s)
1000
S
C+S
UFC+S
UFC+S+MB
UFC+S+E+MB
UFC+C+S+MB
UFC+C+S+MB+E
Fig. 2. The complex viscosity of the samples as a function of frequency for a) single pass compounding, b) compatibilized systems, and c) MB compounding
Frequency (1/s)
0.01 0.1 1 10 100
Ta
n D
elt
a
1
10
S
S+E
UFC+S
UFC+T
UFC+S+E
Frequency (1/s)
0.01 0.1 1 10 100
Ta
n D
elt
a
1
10
S
C+S
UFC+S
UFC+C+S
UFC+C+S+E
UFC+C+S+MB
UFC+C+S+MB+E
Frequency (1/s)
0.01 0.1 1 10 100
Ta
n D
elt
a
1
10
S
C+S
UFC+S
UFC+S+MB
UFC+S+E+MB
UFC+C+S+MB
UFC+C+S+MB+E
Fig. 3. The tan delta of the samples as a function of frequency for a) single pass compounding, b) compatibilized systems, and c) MB compounding
Damping characteristics (tan delta = loss modulus (G'')/storage modulus (G')) of
the UFC-filled HDPE composites were also investigated, and Fig.3 shows the variation in
tan delta according to the frequency. It was evident that at lower frequencies the tan delta
decreased with the incorporation of UFC, which was mainly attributed to the existence of
effective interfacial bonding between the UFC and HDPE matrix. Thus, the viscoelastic
a) b)
c)
a)
b)
c)
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energy dissipation in the composite was limited (Lozano et al. 2004). It was also observed
that the UFC-filled HDPE composites processed with EFM compounding exhibited a
lower tan delta compared to the other composites (Fig. 3c). This implies that the composites
from EFM compounding became substantially less viscous and dissipated less energy
during shear deformation compared to the other composites (Ten et al. 2012).
Frequency (1/s)
0.01 0.1 1 10
Vis
co
sit
y (
Pa
.s)
1000
S
S+E
UFC+S
UFC+T
UFC+S+E
Frequency (1/s)
0.01 0.1 1 10
Vis
co
sit
y (
Pa
.s)
1000
S
C+S
UFC+S
UFC+C+S
UFC+C+S+E
UFC+C+S+MB
UFC+C+S+MB+E
Frequency (1/s)
0.01 0.1 1 10
Vis
co
sit
y (
Pa
.s)
1000
S
C+S
UFC+S
UFC+S+MB
UFC+S+E+MB
UFC+C+S+MB
UFC+C+S+MB+E
Fig. 4. Steady shear viscosity of the samples as a function of shear rate for a) single pass compounding, b) compatibilized systems, and c) MB compounding
Figure 4 shows the apparent viscosity as a function of shear rate at 170 °C for the
neat HDPE and its composites. It was observed that the curves exhibited the characteristics
of typical pseudoplastic materials, and the viscosity of the composites decreased with
increasing shear rate. It is known that the viscous stress predominates over particle
interactions; thus, the alignment is greater and the viscosity lessens at higher shear rates
(Yu et al. 1993). In general, the UFC-filled HDPE composites exhibited higher viscosities
than the neat HDPE at lower shear rates (< 0.1 1/s). Chafidz et al. (2014) discovered a
similar phenomenon that was attributed to the restriction of molecular mobility and the
reduction in free volume induced by the interaction and dispersion of cellulose in the
polypropylene matrix. Similar to the storage modulus, the samples prepared using the SP
compounding method (Fig. 4a) in UFC/S/E composites exhibited a larger melt viscosity,
while those from TSE and SSE were smaller. Owing to the improved UFC-HDPE
interfacial adhesion, the viscosity of the UFC-filled HDPE composites was either higher
or comparable with the addition of coupling agent (Fig. 4b) at all shear rates except for
UFC/C/S/MB in comparison with UFC/S. The effect of MB compounding on the viscosity
of UFC-filled HDPE composites is unclear (Fig. 4c). Overall, the UFC-filled HDPE
composites from the EFM compounding process showed a lower melt viscosity compared
with the other composites at high shear rates. It was unclear what mechanism was
responsible for the reduction in the melt viscosity of the composites at higher shear rates.
Possible reasons are the slip between the HDPE and UFC during high shear flow or a
a) b)
c)
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reduced molecular weight of the HDPE because of the degradation in the presence of UFC
in EFM process. More detailed studies, including rheological studies (capillary rheometer)
and polymer molecular weight characterization, will be required to understand the effect
of the EFM process on the rheological properties (low and high shear rate effect on the
viscosity) of composites (Cho and Paul 2001).
Scanning Electron Microscopy Analysis The SEM images of HDPE composites prepared by UFC are shown in Figs. 5 and
6. It was observed from Fig. 5a that individual large particles were dispersed throughout
the polymer matrix. Figures 5b, 5c, 5d, and 5e show the SEM images for the UFC/T,
UFC/S/E, UFC/S/MB, UFC/S/E/MB compounding methods, respectively. Some
agglomerates separated individual particles and showed better dispersion between the
polymer matrix and UFC, compared with SSE and TSE compounding method. The effect
of the coupling agent was observed in Figs. 6a, 6b, 6c, and 6d. These SEM images show
that using PE-g-MA resulted in better dispersion as discussed previously in the tensile
properties. The reason for improved tensile strength and better dispersion can be explained
by the interaction between the maleic anhydride group, PE-g-MA, and the hydroxyl group
of cellulose through ester and/or hydrogen bonding. Enhanced adhesion and better
dispersion have also been reported by Paunikallio et al. (2003) and Pöllänen et al. (2013)
for viscose fiber and MCC-filled PE and viscose fiber-filled PP composites in the presence
of a coupling agent, respectively.
(a) (b)
(c) (d) (e)
Fig. 5. Scanning electron micrographs of UFC-filled HDPE composites for a) UFC+S, b) UFC+T, c) UFC+S+E, d) UFC+S+MB, and e) UFC+S+MB+E compounding methods without the coupling agent
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(a) (b)
(c) (d)
Fig. 6. Scanning electron micrographs of UFC-filled HDPE composites for a) UFC+C+S, b) UFC+C+S+E, c) UFC+C+S+MB, and d) UFC+C+S+MB+E compounding with the coupling agent
CONCLUSIONS
1. The tensile strength values of the EFM and the coupling agent were higher than those
of the other composites because using a coupling agent with cellulose polymer
composites strengthened the composite. The maximum tensile modulus of elasticity
(0.88 GPa) was obtained using the UFC/C/S/MB/E compounding method. Similar to
impact strength, S+E method without PE-g-MA gave better strain at maximum stress
value. The addition PE-g-MA resulted in better tensile strength. But adding of PE-g-
MA for SSE and S+MB method led a decrease of tensile modulus of elasticity value.
2. When comparing flexural properties, the MB compounding method exhibited an
improvement in the flexural strength and the flexural modulus when using PE-g-MA.
3. The DSC observations showed that the addition of cellulose decreased the melting and
crystallization enthalpies of the composites. The melting and crystallization enthalpies
of UFC/S and UFC/S/E methods increased upon the addition of PE-g-MA.
4. Similar to the storage modulus, the samples prepared using the SP compounding
method in the UFC/S/E composites exhibited greater melt viscosities than composites
from TSE and SSE compounding. The EFM compounding demonstrated a lower tan
delta compared to the other composites. Overall, the UFC-filled HDPE composites
from the EFM compounding method exhibited a lower melt viscosity in comparison
with the other composites at higher shear rates.
5. Based on the SEM imaging, particles dispersed completely into the polymer matrix in
the UFC/S compounding method. Using PE-g-MA provided better dispersion for
compounding methods.
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Boran et al. (2016). “Cellulose HDPE composites,” BioResources 11(4), 8178-8199. 8194
6. It can be concluded from SEM and mechanical results that the EFM device and MB
compounding methods can be successfully employed to provide better mixing,
compounding, and dispersement of cellulose into HDPE matrices.
ACKNOWLEDGMENTS
The authors thank Maine Agricultural and Forest Experiment Station (MAFES)
project ME09615-08MS and the Wood Utilization Research Hatch project for funding. The
Council of Higher Education (YOK) and Karadeniz Technical University have been
acknowledged for the scholarship of the postdoctoral researcher Sevda Boran to do this
study at the University of Maine. The authors would like to thank Alex Nash and Chris
West for the sample preparation and characterization. This is the 3495th paper of the Maine
Agricultural and Forest Experiment Station.
REFERENCES CITED
Abdul Khalil, H. P. S., Davoudpour, Y., Nazrul Islam, M., Mustapha, A., Sudesh, K.,
Dungani, R., and Jawaid, M. (2014). “Production and modification of nanofibrillated
cellulose using various mechanical process: A review,” Carbohydrate Polymers 99,
649-665. DOI: 10.1016/j.carbpol.2013.08.069
Araujo, J. R., Waldman, W. R., and de Paoli, M. A. (2008). “Thermal properties of high
density polyethylene composites with natural fibres: Coupling agent effect,” Polymer
Degradation and Stability 93(10), 1770-1775. DOI:
10.1016/j.polymdegradstab.2008.07.021
ASTM D 256-10 (2010).“Standard test methods for determining the izod pendulum
impact resistance of plastics,” ASTM International, West Conshohocken, PA.
ASTM D 5229 M 14 (2014). “Standard test method for moisture absorption properties
and equilibrium conditioning of polymer matrix composite materials,”ASTM
International, West Conshohocken, PA.
ASTM D638-10 (2010). “Standard test method for tensile properties of plastics,” ASTM
International, West Conshohocken, PA.
ASTM D 790-10 (2010). “Standard test methods for flexural properties of unreinforced
and reinforced plastics and electrical insulating materials, test method 1, procedure
A,” ASTM International, West Conshohocken, PA.
Balatinecz, J. J., Khavkine, M. I., Law, S., and Kovac, V. (1999). “Properties of
polyolefin composites with blends of wood flour and coal ash,” in: Proceedings of the
Fifth International Conference on Wood fiber-Plastic Composites, Forest Products
Society, May 26-27, Madison, WI, pp. 235-240.
Bataille, P., Allard, P., Cousin, P., and Sapieha, S. (1990). “Interfacial phenomena in
cellulose/polyethylene composites,” Polymer Composites 11(5), 301-304. DOI:
10.1002/pc.750110508
Boran, S., Kiziltas, A., Kiziltas, E. E., and Gardner, D. J. (2016). “The comparative study
of different mixing methods for microcrystalline cellulose/polyethylene composites,”
International Polymer Processing 31(1), 92-103. DOI: 10.3139/217.3156
Botros, M. (2003). “Development of new generation coupling agents for wood-plastic
composites,” Equistar Chemicals LP, New Orleans, LA.
PEER-REVIEWED ARTICLE bioresources.com
Boran et al. (2016). “Cellulose HDPE composites,” BioResources 11(4), 8178-8199. 8195
Bourry, D., Godbille, F., Khayat, R. E., Luciani, A., Picot, J., and Utracki, L. A. (1999).
“Extensional flow of polymeric dispersions,” Polymer Engineering and Science
39(6), 1072-1086. DOI:10.1002/pen.11495
Caulfield, D. F., Jacobson, R. E., Sears, K. D., and Underwood, J. H. (2001). “Fiber
reinforced engineering plastics,” in: Proceedings of the Second International
Conference on Advanced Engineered Wood Composites, August 14-16, Maine, ME,
pp. 6.
Chafidz, A., Kaavessina, M., Al-Zahrani, S., and Al-Otaibi, M. N. (2014). “Rheological
and mechanical properties of polypropylene/calcium carbonate nanocomposites
prepared from masterbatch,” Journal of Thermoplastic Composite Materials 29(5),
593-622. DOI: 10.1177/0892705714530747
Cho, J. W., and Paul, D. R. (2001). “Nylon 6 nanocomposites by melt compounding,”
Polymer 42(3), 1083-1094. DOI: 10.1016/S0032-3861(00)00380-3
Dennis, H. R., Hunter, D. L., Chang, D., Kim, S., White, J. W., Cho, J. W., and Paul, D.
R. (2001). “Effect of melt processing conditions on the extent of exfoliation in
organoclay-based nanocomposites,” Polymer 42(23), 9513-9522. DOI:
10.1016/S0032-3861(01)00473-6
Endo, R., Saito, T., and Isogai, A. (2013). “TEMPO-oxidized cellulose
nanofibril/poly(vinyl alcohol) composites drawn fibers,” Polymer 54(2), 935-941.
DOI: 10.1016/j.polymer.2012.12.035
Etelaaho, P., Nevalainen, K., Suihkonen, R., Vuorinen, J., Hanhi, K., and Jarvela, P.
(2009). “Effects of direct melt compounding and masterbatch dilution on the structure
and properties of nanoclay-filled polyolefins,” Polymer Engineering and Science
49(7), 1438-1446. DOI: 10.1002/pen.21270
Hatzikiriakos, S. G., Rathod, N., and Muliawan, E. B. (2005). “The effect of nanoclays
on the processibility of polyolefins,” Polymer Engineering and Science 45(8), 1098-
1107. DOI: 10.1002/pen.20388
Henriksson, M., Henriksson, G., Berglund, L. A., and Lindström, T. (2007). “An
environmentally friendly method for enzyme-assisted preparation of microfibrillated
cellulose (MFC) nanofibers,” European Polymer Journal 43(8), 3434-3441. DOI:
10.1016/j.eurpolymj.2007.05.038
Herrera-Franco, P. J., and Aguilar-Vega, M. J. (1997). “Effect of fiber treatment on the
mechanical properties of LDPE-henequen cellulosic fiber composites,” Journal of
Applied Polymer Science 65(1), 197-207. DOI: 10.1002/(SICI)1097-
4628(19970705)65:1<197::AID-APP24>3.0.CO;2-#
Hitoshi, T., and Akira, A. (2007). “Characterization of ‘green’ composites reinforced by
cellulose nanofibers,” Key Engineering Materials 334-335, 389-392. DOI:
10.4028/www.scientific.net/KEM.334-335.389
Ismail, H., Mega, L., and Abdul Khalil, H. P. S. (2001). “Effect of a silane coupling agent
on the properties of white rice husk ash-polypropylene/natural rubber composites,”
Polymer International 50(5), 606-611. DOI: 10.1002/pi.673
JMP Statistical Discovery Software Version 8, Cary, North Carolina, USA.
Joo, M., Auras, R., and Almenar, E. (2011). “Preparation and characterization of blends
made of poly (l-lactic acid) and β-cyclodextrin: Improvement of the blend properties
by using a masterbatch,” Carbohydrate Polymers 86(2), 1022-1030. DOI:
10.1016/j.carbpol.2011.05.058
PEER-REVIEWED ARTICLE bioresources.com
Boran et al. (2016). “Cellulose HDPE composites,” BioResources 11(4), 8178-8199. 8196
Josefsson, G., Berthold, F., and Gamstedt, E. K. (2014). “Stiffness contribution of
cellulose nanofibrils to composite materials,” International Journal of Solids and
Structures 51(5), 945-953. DOI:10.1016/j.ijsolstr.2013.11.018
Khalil, H. P. S., Bhat, A. H., and Yusra, A. F. I. (2012). “Green composites from
sustainable cellulose nanofibrils: A review,” Carbohydrate Polymer 87(2), 963-979.
DOI: 10.1016/j.carbpol.2011.08.078
Kiziltas, A., Gardner, D. J., Han, Y., and Yang, H.-S. (2010). “Determining the
mechanical properties of microcrystalline cellulose (MCC)-filled PET-PTT blend
composites,” Wood and Fiber Science 42(2), 165-176.
Kiziltas, A., Nazari, B., Gardner, D. J., and Bousfield, D. W. (2013). “Polyamide 6-
cellulose composites: Effect of cellulose composition on melt rheology and
crystallization behavior,” Polymer Engineering and Science 54(4), 739-746. DOI:
10.1002/pen.23603
Kiziltas, A., Nazari, B., Kiziltas, E. E., Gardner, D. J., Han, Y., and Rushing, T. S.
(2016a). “Cellulose nanofiber-polyethylene nanocomposites modified by polyvinyl
alcohol,” Journal of Applied Polymer Science 133(6), 1-8. DOI: 10.1002/app.42933
Kiziltas, A., Nazari, B., Erbas Kiziltas, E., Gardner, D. J., Han, Y., and Rushing, T. S.
(2016b). “Method to reinforce polylactic acid with cellulose nanofibers via a
polyhyrdoxybutyrate carrier system,” Carbohydrate Polymers 140, 393-399. DOI:
10.1016/j.carbpol.2015.12.059
Kvien, I., Tanem, B. S., and Oksman, K. (2005). “Characterization of cellulose whiskers
and their nanocomposites by atomic force and electron microscopy,”
Biomacromolecules 6(6), 3160-3165. DOI: 10.1021/bm050479t
Kvien, I., and Oksman, K. (2007). “Orientation of cellulose nanowhiskers in polyvinyl
alcohol,” Applied Physics A87(4), 641-643. DOI: 10.1007/s00339-007-3882-3
Lee, S. H., Kim, M. W., Kim, S. H., and Youn, J. R. (2008). “Rheological and electrical
properties of polypropylene/MWCNT composites prepared with MWCNT
masterbatch chips,” European Polymer Journal 44(6), 1620-1630. DOI:
10.1016/j.eurpolymj.2008.03.017
Li, Y.-C., and Chen, G.-H. (2007). “HDPE/expanded graphite nanocomposites prepared
via masterbatch process,” Polymer Engineering and Science 47(6), 882-888. DOI:
10.1002/pen.20772
Li, J., Ton-That, M. T., Leelapornpisit, W., and Utracki, L. A. (2007). “Melt
compounding of polypropylene- based clay nanocomposites,” Polymer Engineering
and Science 47(6), 1447-1458. DOI: 10.1002/pen.20841
Lopez-Quintanilla, M. L., Sanchez-Valdes, S., Ramos de Valle, L. F., and Medellin-
Rodriguez, F. J. (2005). “Effect of some compatibilizing agents on clay dispersion of
polypropylene-clay nanocomposites,” Journal of Applied Polymer Science 100(6),
4748-4756. DOI: 10.1002/app.23262
Lozano, K., Yang, S., and Jones, R. E. (2004). “Nanofiber toughened polyethylene
composites,” Carbon 42(11), 2329-2331. DOI: 10.1016/j.carbon.2004.03.021
Luciani, A., and Utracki, L. A. (1996). “The extensional flow mixer, EFM,” International
Polymer Processing 11(4), 299. DOI: 10.3139/217.960299
Ma, L., Zhang, Y., Meng, Y., Anusonti-Inthra, P., and Wang, S. (2015). “Preparing
cellulose nanocrystal/acrylonitrile-butadiene-styrene nanocomposites using the
master-batch method,” Carbohydrate Polymers 125, 352-359. DOI:
10.1016/j.carbpol.2015.02.062
PEER-REVIEWED ARTICLE bioresources.com
Boran et al. (2016). “Cellulose HDPE composites,” BioResources 11(4), 8178-8199. 8197
Mariano, M., Kissi, N. E., and Dufresne, A. (2015). “Melt processing of cellulose
nanocrystal reinforced polycarbonate from a masterbatch process,” European
Polymer Journal 69, 208-223. DOI: 10.1016/j.eurpolymj.2015.06.007
Mathew, A. P., Oksman, K., and Sain, M. (2005). “Mechanical properties of
biodegradable composites from poly lactic acid (PLA) and microcrystalline cellulose
(MCC),” Journal of Applied Polymer Science 97(5), 2014-2025. DOI:
10.1002/app.21779
Mirabella, F. M., and Bafna, A. (2002). “Determination of the crystallinity of
polyethylene/α-olefin copolymers by thermal analysis: Relationship of the heat of
fusion of 100% polyethylene crystal and the density,” Journal of Polymer Science
Part B: Polymer Physics 40(15), 1637-1643. DOI: 10.1002/polb.10228
Mukherjee, T., Sani, M., Kao, N., Gupta, R. K., Quazi, N., and Bhattacharya, S. (2013).
“Improved dispersion of cellulose microcrystals in polylactic acid (PLA) based
composites applying surface acetylation,” Chemical Engineering Science 101, 655-
662. DOI: 10.1016/j.ces.2013.07.032
Nguyen, X. Q., and Utracki, L. A. (1995). “Extensional flow mixer,” U.S. Patent
545110619.
Ozen, E., Kiziltas, A., Erbas Kiziltas, E., and Gardner, D. J. (2013). “Natural fiber blend-
nylon 6 composites,” Polymer Composites 34(4), 544-553. DOI: 10.1002/pc.22463
Panaitescu, D. M., Notingher, P. V., Ghiurea, M., Ciuprina, F., Paven, H., Iorga, M., and
Florea, D. J. (2007a). “Properties of composite materials from polyethylene and
cellulose microfibrils,” Journal of Optoelectronics and Advanced Materials 9(8),
2524-2528.
Panaitescu, D. M., Donescu, D., Bercu, C., Vuluga, D. M., Iorga, M., and Ghiurea, M.
(2007b). “Polymer composites with cellulose microfibrils,” Polymer Engineering and
Science 47(8), 1228-1234. DOI: 10.1002/pen.20803
Pandey, J. K., Nakagaito, A. N., and Takagi, H. (2013). “Fabrication and applications of
cellulose nanoparticle-based polymer composites,” Polymer Engineering and Science
53(1), 1-8. DOI: 10.1002/pen.23242
Paunikallio, T., Kasanen, J., Suvanto, M., and Pakkanen, T. T. (2003). “Influence of
maleated polypropylene on mechanical properties of composites made of viscose
fiber and polypropylene,” Journal of Applied Polymer Science 87(12), 1895-1900.
DOI: 10.1002/app.11919
Petersson, L., and Oksman, K. (2006). “Biopolymer based nanocomposites: Comparing
layered silicates and microcrystalline cellulose as nanoreinforcement,” Composites
Science and Technology 66(13), 2187-2196. DOI: 0.1016/j.compscitech.2005.12.010
Pöllänen, M., Suvanto, M., and Pakkaneni, T. T. (2013). “Cellulose reinforced high
density polyethylene composites-morphology, mechanical and thermal expansion
properties,” Composites Science and Technology 76(4), 21-28. DOI:
10.1016/j.compscitech.2012.12.013
Prashantha, K., Soulestin, J., Lacrampe, M. F., Krawczak, P., Dupin, G., and Claes, M.
(2009). “Masterbatch-based multi-walled carbon nanotube filled polypropylene
nanocomposites: Assessment of rheological and mechanical properties,” Composites
Science and Technology 69(11-12), 1756-1763. DOI:
10.1016/j.compscitech.2008.10.005
Ramires, E. C., and Dufresne, A. (2011). “A review of cellulose nanocrystals and
nanocomposites,” TAPPI Journal 10(4), 9-16.
Rauwendaal, C. (1998). “Polymer mixing: A self-study guide,” Hanser, Cincinnati, OH.
PEER-REVIEWED ARTICLE bioresources.com
Boran et al. (2016). “Cellulose HDPE composites,” BioResources 11(4), 8178-8199. 8198
Rauwendaal, C., Rios, A., Osswald, T. A., Gramann, P., Davis, B., Noriega, M. P., and
Estrada, O. A. (1999). “Experimental study of a new dispersive mixer,” in:
Proceedings from the 57th SPE ANTEC, May 2-6, Atlanta, GA.
Sdrobiş, A., Daire, R. N., Totolin, M., Cazacu, G., and Vasile, C. (2012). “Low density
polyethylene composites containing cellulose pulp fibers,” Composites Part B:
Engineering 43(4), 1873-1880. DOI: 10.1016/j.compositesb.2012.01.064
Shao, X., He, L., and Ma, L. (2015). “Study on tensile behavior of natural fiber
reinforced pp composites,” in: The 2nd International Forum on Electrical
Engineering and Automation (IFEEA 2015), December 26-27, pp. 265-268.
Shumigin, D., Tarasova, E., Krumme, A., and Meier, P. (2011). “Rheological and
mechanical properties of poly(lactic) acid/cellulose and LDPE/cellulose composites,”
Materials Science 17(1), 32-37. DOI: 10.5755/j01.ms.17.1.245
Spoljaric, S., Genovese, A., and Shanks, R. A. (2009). “Polypropylene-microcrystalline
cellulose composites with enhanced compatibility and properties,” Composites Part
A: Applied Science and Manufacturing 40(6-7), 791-799. DOI:
10.1016/j.compositesa.2009.03.011
Šumigin, D., Tarasova, E., Krumme, A., and Viikna, A. (2012). “Influence of cellulose
content on thermal properties of poly(lactic) acid/cellulose and low-density
polyethylene/cellulose composites,” Proceedings of the Estonian Academy of
Sciences 61(3), 237-244.
Tajeddin, B., Rahman, R. A., and Abdullah, L. C. (2009). “Mechanical and morphology
properties of kenaf cellulose/LDPE biocomposites,” Journal of Agriculture and
Environmental Sciences 5(6), 777-785.
Ten, E., Bahr, D. F., Li, B., Jiang, L., and Wolcott, M. P. (2012). “Effects of cellulose
nanowhiskers on mechanical, dielectric, and rheological properties of poly (3-
hydroxybutyrate-co-3-hydroxyvalerate)/cellulose nanowhisker composites,”
Industrial and Engineering Chemistry Research 51(7), 2941-2951. DOI:
10.1021/ie2023367
Tokihisa, M., Yakemeto, K., Sakai, T., Utracki, L. A., Sepehr, M., and Simard, L. Y.
(2006). “Extensional flow mixer for polymer nanocomposites,” Polymer Engineering
and Science 46(8), 1040-1050. DOI:10.1002/pen.20542
Treece, M. A., Zhang, W., Moffitt, R. D., and Oberhauser, J. P. (2007). “Twin-screw
extrusion of polypropylene-clay nanocomposites: Influence of masterbatch
processing, screw rotation mode, and sequence,” Polymer Engineering and Science
47(6), 898-911. DOI: 10.1002/pen.20774
Utracki, L. A. (2003). “Polymeric nanocomposites: Compounding and performance,” in:
Polymer Nanocomposites, Boucherville, QC, Canada, October 6-8, pp.1-10.
Utracki, L. A. (2007). “Polymeric nanocomposites: Compounding and performance,” in:
Anais do 9° CongressoBrasileiro de Polimeros,October 7, pp.1-10.
Utracki, L.A., Luciani, A., and Bourry, J. J. (2003). “Extensional flow mixer,” US Patent
6550956.
Volk, N., He, R., and Magniez, K. (2015). “Enhanced homogeneity and interfacial
compatibility in melt-extruded cellulose nano-fibers reinforced polyethylene via
surface adsorption of poly(ethylene glycol)-block-poly(ethylene) amphiphiles,”
European Polymer Journal 72, 270-281. DOI: 10.1016/j.eurpolymj.2015.09.025
Walther, A., Bjurhager, I., Malho, J.-M., Pere, J., Ruokolainen, J., Berglund, L. A., and
Ikkala, O. (2010). “Large-area, lightweight and thick biomimetic composites with
PEER-REVIEWED ARTICLE bioresources.com
Boran et al. (2016). “Cellulose HDPE composites,” BioResources 11(4), 8178-8199. 8199
superior material properties via fast, economic, and green pathways,” Nano Letters
10(8), 2742-2748. DOI: 10.1021/nl1003224
Wang, W. and Zloczower, I. M. (2001). “Dispersive and distributive mixing
characterization in extrusion equipment,” in: Antec 2001 Conference Proceedings,
May 6-10, Dallas, TX.
Yang, H.-S., and Gardner, D. J. (2011). “Morphological characteristics of cellulose
nanofibril-filled polypropylene composites,” Wood and Fiber Science 43(2), 215-224.
Yang, H.-S., Gardner, D. J., and Nader, J. W. (2011). “Characteristic impact resistance
model analysis of cellulose nanofibril-filled polypropylene composites,” Composites
Part A: Applied Science and Manufacturing 42(12), 2028-2035. DOI:
10.1016/j.compositesa.2011.09.009
Yu, Z., Ou, Y., and Feng, Y. (1993). “Effects of coupling agents on the rheological
behavior of kaolin filled polyamide 6,” Chinese Journal of Polymer Science 11(1),
59-66.
Article submitted: May 25, 2016; July 18, 2016; Revised version received: July 21, 2016;
Accepted: July 22, 2016; Published: August 9, 2016.
DOI: 10.15376/biores.11.4.8178-8199